For high data rate writer application, one of the requirements is to have fast saturation and low inductance to induce short rise time. On the other hand, a low fly height for high areal density recording beyond 60 GB is needed in order to have better head performance. Many reliability problems are, however, associated with this low fly height. Problems such as thermal pole tip protrusion induced by thermal mismatch between alumina and pole materials during the writing process will create a head-disk interface problem and eventually will damage the read head. One of the solutions to reducing thermal pole tip protrusion is to reduce DC coil resistance of the writer so that less heat is generated during the writing process. Additionally, lower DC coil resistance improves the coil's thermal reliability.
FIG. 1 is a schematic cross-section through a typical stitched writer design having two coil layers. Seen in FIG. 1 are GMR read head 10, read head lower shield 11, read head upper shield 12, write head bottom pole 13 (P1), lower coil insulation 14, seed layers 15 and 17, write gap 16, stitched top pole 19, lower coil 20, upper coil 21, upper coil insulation 22, top pole 23, coil lead 24, and alumina layer 25
The main drawback of this 2 layer coil stitched writer structure is its high DC coil resistance. This is a result of the prior art processes used for its manufacture. In particular, because of the small size and internal spacings of the coils, the preferred material for enclosing and electrically isolating the coils has been hard baked photoresist. This material is well suited to filling in tiny openings and is soft enough to accommodate volume changes in the coils due to thermal expansion while they are operating at maximum power. Present processes used for planarizing a cavity filled with a coil and hard baked photoresist require that a significant amount of the thickness of the coils be removed. This, in turn, increases the DC resistance of a given coil having a given number of turns leading to a degradation of its performance.
In this invention, we describe a novel two layer coil structure with low DC coil resistance for short yoke length stitched writer.
A routine search of the prior art was performed with the following references of interest being found:
In U.S. Pat. No. 6,317,288, Sasaki describes a device having two coils while in U.S. Pat. No. 6,466,404, Crue Jr. et al disclose a device having a coil embedded in the first pole. U.S. Pat. No. 6,396,660 (Jenson et al) shows a device wherein a coil is situated atop a heat sink and in U.S. Pat. No. 6,339,523 Santini teaches a device having two coils, but the coils are not aligned. Hong et al show, in U.S. Pat. No. 6,466,401, a device having interlaced coils.